What is chronic traumatic encephalopathy?

An autopsy performed one year after Kansas City Chiefs linebacker Jovan Belcher fatally shot his 22-year-old girlfriend and killed himself in front of his coach and the team's general manager found signs of chronic traumatic encephalopathy (CTE).

Recently, former quarterback Brett Favre says he's suffering memory lapses, which can be a sign of CTE. Find out more about chronic traumatic encephalopathy, the disease several NFL pros claim they are now suffering from due to hits on the field.

Chronic traumatic encephalopathy (CTE) is a progressive degenerative disease, diagnosed post-mortem in individuals with a history of multiple concussions and other forms of head injury.

Researchers say CTE has a clear environmental cause (repeated brain trauma) rather than a genetic cause. In other words, CTE is the only preventable form of dementia.

In 2008, the Sports Legacy Institute joined with the Boston University School of Medicine to form the Center for the Study of Traumatic Encephalopathy (CSTE), where many brain trauma cases are studied.

CTE has been most commonly found in professional athletes participating in American football, boxing, professional wrestling and other contact sports.

The condition is also found in professional athletes who have played ice hockey and, to a lesser extent, those involved in military service.

NFL great Junior Seau's death prompted discussions about brain trauma.

There is no proof that Seau suffered from CTE, but reports say that he had acted erratically in recent years, getting arrested and driving an SUV off a 100-foot cliff. According to CNN, he’d told a friend he was worried about football-related brain damage.

John Mackey, one of NFL football's great tight ends, died in 2011 of frontotemporal dementia, a syndrome similar to CTE that involves degeneration of the brain.

The NFL Players Association initially refused to pay Mackey a disability income due to there not being a proven link between brain injury and playing football. The league and the NFL Players Association have responded with the "88 plan" – named after Mackey's number.

The plan provides $88,000 per year for nursing home care and up to $50,000 annually for adult day care.

Hockey Great Reg Fleming was the first hockey player known to have CTE. This discovery was announced in December 2009, six months after Fleming's death.

In 2007, WWE wrestler Chris Benoit had his brain examined after he killed his wife and son before committing suicide. Originally the tragedy was thought to be due to the abuse of anabolic steroids. However, a brain biopsy identified pathognomonic brain tissue changes of CTE.

In 2011, former Chicago Bears safety Dave Duerson, 50, shot himself in the chest, leaving a suicide note donating his brain to science. Boston University pathologists found lesions in Duerson’s brain.

Duerson's was the 15th NFL brain they dissected. They found similar damage in all but one of the 15.